1. Field of Invention
This invention relates to gauges for measuring liquid volume in liquid containers and tanks. More particularly, the invention relates to a dynamic gauge that uses signals that permit the installation of transducers and/or sensors on the outside surface of the containers.
2. Description of Prior Art
Other systems use capacitance probes, float actuated electro-mechanical devices, or differential pressure sensors immersed in the fluid. Ultrasonic transducer systems have been inserted in the top of liquid tanks to measure liquid level. Similarly, acoustic systems have used transducers inserted in the tank to measure the volumetric change as fluid is removed from a tank. Strain gauges have been used on the exterior of the tank to measure the liquid weight or the volume of liquid remaining in the tank. Exterior mounting, or non-invasiveness, is obviously a desirable attribute, but strain gauges are expensive and have reliability problems even in environments that are only moderately hostile. All invasive systems, i.e. those that require the sensor or transducer to be inserted in the liquid container, have higher installation costs and usually are relatively unreliable, more expensive, and require more maintenance. These systems do not lend themselves to multi-tank applications easily.
Transducers, even ones that I expected to work accurately and repeatably in test, would often perform satisfactorily for awhile, and then would unaccountably degrade in performance. On inspection, the transducers appeared to be normal, but their performance was erratic. Such performance would be unacceptable in many of the intended applications, such as truck and marine fuel tanks, so it was necessary to discover and eliminate the cause of the erratic transducer performance, which I have done.